fix(audit-verification): regressions found in post-Tier-6 review

Two parallel reviews of the Tier 0–6 work surfaced one CRITICAL
regression and a handful of remaining cross-tenant gaps that the
original audit didn't enumerate. All fixed here:

CRITICAL
* document-reminders.processReminderQueue — the new bulk-fetch
  leftJoin to documentTemplates was scoped on `templateType` alone.
  Templates of the same type exist in every port; the cartesian
  explosion would have fired one Documenso reminder PER matching
  template-row per cron tick (a 5-port deploy = 5 reminders to the
  same signer per cycle). Added eq(documentTemplates.portId, portId)
  to the join.
* All five remaining Documenso webhook handlers (RecipientSigned /
  Completed / Opened / Rejected / Cancelled) accept and require an
  optional portId now, with a shared resolveWebhookDocument() helper
  that refuses to mutate when the lookup is ambiguous across tenants
  without a resolved port. Tier 5's port-scoping was applied only to
  Expired; the route now forwards the matched portId to every
  handler. Tightens the WHERE clauses on subsequent UPDATEs to (id,
  portId) for defense-in-depth.

HIGH
* verifyDocumensoSecret rejects when `expected` is empty —
  timingSafeEqual(0-bytes, 0-bytes) was returning true, so a dev env
  with a blank DOCUMENSO_WEBHOOK_SECRET would accept a request whose
  X-Documenso-Secret header was also missing/empty.
  listDocumensoWebhookSecrets skips the env entry when blank.
* /api/public/health — the website-intake-secret comparison was a
  string `===` (not constant-time). Switched to timingSafeEqual via
  Buffer.from().

MEDIUM
* server.ts SIGTERM ordering — Socket.io closes BEFORE the HTTP
  drain so long-poll websockets stop holding the server open past
  the compose stop_grace_period.
* /api/v1/me PATCH preferences merge — allow-list filter on the
  merged JSONB so legacy rows from the old .passthrough() era stop
  silently re-shipping their bloat to disk.

Migration fixes (deploy-blocking)
* 0041 referenced `port_role_overrides.permissions` (column is
  `permission_overrides`) — overrides are partial JSONB and don't
  need backfilling at all (deepMerge resolves edit from the base
  role). Removed the override UPDATEs entirely.
* 0042 switched all FK + CHECK adds to NOT VALID + VALIDATE so the
  brief table-lock phase is decoupled from the row-scan validation,
  giving a cleaner abort-and-restart story if a constraint catches
  dirty production data. Added a pre-cleanup UPDATE for
  invoices.billing_entity_id = '' rows (backfills from clientName,
  falls back to the row id) so the new non-empty CHECK passes on a
  dirty table.

Test status: 1175/1175 vitest, tsc clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/app/api/public/health/route.ts

@@ -1,4 +1,5 @@
 import { NextRequest, NextResponse } from 'next/server';
+import { timingSafeEqual } from 'node:crypto';
 
 import { env } from '@/lib/env';
 
@@ -19,8 +20,20 @@ import { env } from '@/lib/env';
 export function GET(req: NextRequest): Response {
   const expected = env.WEBSITE_INTAKE_SECRET;
   const provided = req.headers.get('x-intake-secret');
+  // Use timingSafeEqual rather than a `===` comparison — string equality
+  // is not constant-time and lets a remote attacker enumerate the secret
+  // byte-by-byte via response-time differences.
   const matched =
-    expected && provided && provided.length === expected.length && provided === expected;
+    !!expected &&
+    !!provided &&
+    provided.length === expected.length &&
+    (() => {
+      try {
+        return timingSafeEqual(Buffer.from(provided), Buffer.from(expected));
+      } catch {
+        return false;
+      }
+    })();
 
   if (!matched) {
     return NextResponse.json(